The present invention relates to new fungicidal compositions comprising a stabilized aqueous solution of the salt of a phosphorous acid ester as an active ingredient, and methods of treating fungal diseases in plants with these compositions.
Subject matter relating to this application is described in French Pat. No. 2,254,276, which corresponds to U.S. Pat. No. 4,139,616, and is hereby incorporated by reference. French Pat. No. 2,254,276 describes the use of compositions containing the metal salt of an alkyl ester of phosphorous acid, in particular, aluminum tris-ethylphosphonate, to combat fungal diseases in plants. The compositions of French Pat. No. 2,254,276 contain, as the active ingredient, at least one salt of an alkyl-phosphorous acid corresponding to the general formula: ##STR1## in which R is an optionally halogenated or nitrated, linear or branched alkyl radical containing from 1 to 18 carbon atoms and preferably from 1 to 8 carbon atoms, an optionally halogenated alkenyl or alkinyl radical, an alkoxy alkyl radical, an alkenoxy alkyl radical, the hydrocarbon portion of these four types of radicals containing from 1 to 8 and preferably from 1 to 5 carbon atoms, a cyclohexyl radical, an optionally substituted aryl radical, preferably phenyl, or aryl alkyl radical, preferably phenyl alkyl, or a heterocyclic radical optionally attached to the oxygen through an aliphatic chain, preferably tetrahydrofurfuryl, M represents a hydrogen atom, ammonium cation, ammonium substituted by 1 to 4 alkyl or hydroxy alkyl radicals containing from 1 to 5 carbon atoms or 1 to 2 cyclohexyl radicals of a phenyl radical, or a cation of a metal from the group comprising the alkali metals, preferably sodium and potassium, alkaline earth metals, preferably magnesium, barium, calcium, and polyvalent metals such as, preferably, zinc, manganese, copper (I) and (II), iron, nickel, aluminum, and n is an integer equal to the valency of M.
These compositions have been found to be effective against many phytophagous fungi, such as Phycomycetes, particularly Plasmopara viticola and various Phytophthora. In practice, aluminum tris-ethyl-phosphonate or aluminum ethyl phosphite known commercially as Phosethyl Al, is applied to a plant in the form of a suspension of a wettable powder by spraying the leaves. Although the treatment is quite effective for protecting vines against fungal attack, the effectiveness of this treatment against fungal diseases in tropical plants has been less than desirable. It has been found that it takes too long a time to cure a plant which has been attacked, often heavily, by fungi of the Phytophthora type, such as Phytophthora cinnamomi which causes the rotting of avocado and citrus fruit trees.
The reason that the spray treatment has not been very effective is because the amount of active ingredient absorbed via the leaves of a plant is relatively small. This small amount is insufficient if the plant has already been attacked by fungi and has to be cured. This necessitates more spraying, making the treatment prohibitively expensive and very slow. At times, if the plant has been severely attacked by fungi even multiple treatments are inadequate.
Moreover, Phosethyl Al undergoes rapid hydrolysis in an aqueous medium, and over a period of time there is a substantial and progressive decrease in the amount of active ingredient in the solution. It is thus impossible to have concentrated aqueous compositions which are stable over a period of time.